Windarchers have an atrocious hurricane. 20b on a shadower you wouldn't get too far unless you found some pretty amazing deals. Do you have any goals in mind or any expectations as to what 20b would allow you to achieve?
With 20b on a regular server, that will get you maybe 500k-700k range if you spend wisely. True, that'll be better than a night lord or a dual blade at that range, but definitely not where shadowers outdamage a db. That is probably 300-400b. Wind archer would be the way to go.
Both don't matter too much on reboot, but wind archer would still probably edge over shadower in most situations going by pure damage, but shadowers have their own benefits too.
Let me break it down for someone whos like me. They can't pick a class so they make everyone.
Dex% is laughably cheaper than Luk%. And if you have any other bowman you can have bonus proc to final attack. Unless it was damage added to final attack...I can't remember atm but it was good. Best of luck and may the deals be with you